Method and arrangement for preventing the locking of wheels of a commercial vehicle

ABSTRACT

Pulses generated in synchronism with the rotation of the wheel are reshaped into measuring pulses having a steep leading edge and a slowly decreasing trailing edge. The pulses overlap. The instantaneous value of a measuring pulse at the beginning of a subsequent measuring pulse is compared with the corresponding value of a preceding measuring pulse, and a terminating signal terminating the application of the brakes, is furnished when the difference between two sequential so-determined instantaneous values exceed a predetermined difference.

States Patent aumann [45] n1. 1972 [54] METHOD AND ARRANGEMENT FOR3,235,036 2/1966 Meyer et a1 ..l88/l8l A PREVENTING THE LOCKING3,245,213 4/1966 Thompson et al. .....303/21 A WHEELS OF A COMMERCIAL3,401,984 9/1968 Williams et al. ..303/21 A 3,450,444 6/ l969 Ballard...l88/l8l C VEHICLE 3,511,542 /1970 Fielek, Jr. ..303/21 A [72]Inventor: Gunther Baumann, Stuttgart, Germanv Primary Examiner MiltonBuchler 73] Assignee: Robert Bosch Gmbli, Stuttgart, Germany AssistantExaminer-Stephen G. Kunin Filed: Nov. 1969 Attorney-M1chaelS.Str1ker[2]] Appl. No.: 878,685

[30] Foreign Application Priority Data Nov. 26, l968 Germany ..P 18950.7

[52] U.S. Cl ..303/21 CF, 188/181 C, 303/ 51 1111. Cl. ..Bt 8/08 [58]Field of Search ..l88/l8l; 303/21, 20; 307/;

[56] References Cited UNITED STATES PATENTS 3,026,148 3/1962 Ruof"..303/21c15 ference PuLsE GENERATOR PULSE 51111 01 "sum l l l I1151511111111; PULSE 51111011 [5 7] ABSTRACT 16 Claims, 3 DrawingFigures IQMULTIVIBRATOR (MONOSIABLE) COMPARATOR 77 F IG. 7

IMENTED MAN 2 8 I972 INVENTOR Gunther BAUMANN y 070144 M/ flukhis/ATTORNEY METHOD AND ARRANGEMENT FOR PREVENTING TI-IE LOCKING OEWll-IEELS OE A COMMERCIAL VEHICLE BACKGROUND OF THE INVENTION Thisinvention relates to a method and arrangement for preventing the lockingof the wheels of a commercial vehicle during a braking process. Inparticular, it relates to a method and arrangement wherein pulses aregenerated by the rotation of wheels, and circuits are provided whichrespond to these pulses and generate a terminating signal terminatingthe application of the brakes when it is indicated that the wheels arebeginning to lock.

Traffic safety depends to a great extent on the proper functioning ofthe brakes of commercial vehicles. For safe braking, the vehicle shouldnot depart from its course during the braking operation and must bestopped in the shortest possible distance. These requirements can onlybe met if the wheels do not lock during a braking process. Blocking ofthe wheels indicates that the tire slips on the street. This is known asskidding and it is well known that the coefficient of resistance is lowduring a skid. Thus thebraking action is decreased. Furthermore, thevehicle is also more liable to side-wise movement, since the coefficientof resistance in the side-wise direction is also decreasedsubstantially.

'A conventional way of solving this problem is to connect a toothed gearof magnetically conductive material with the wheels of the vehicle andto attach pulse generating means to the body of the vehicle. When such atoothed wheel moves past the pulse generating means, the air gap betweenthe pulse generating means and the toothed gear decreases, changing theinductivity of the section. The change in inductivity is then used togenerate the pulse. Thus the pulse repetition rate of the so-generatedpulses corresponds to the speed of the wheel. If these pulses areintegrated, it is possible to derive a value indicative for theacceleration. When a wheel is locked, changes in the value indicative ofthe acceleration occur, which in turn are indicative of a locking of thewheels. However, this integration of pulses has the disadvantage that,due to the required time constant, a not inconsiderable delay occursbetween the beginning of the actual braking of the wheel and thetermination of the braking action.

SUMMARY OF THE INVENTION An object of this invention is to furnish amethod and arrangement for preventing the locking of wheels incommercial vehicles, without the above-mentioned drawbacks.

In accordance with the present invention, a pulse sequence is generatedin synchronism with the rotation of the wheels. The so-derived pulsesare reshaped into measuring pulses having an amplitude varying as apredetermined function of time. The beginning of any measuring pulseprecedes in time termination of a preceding measuring pulse.=Theinstantaneous value of a measuring pulse at a predetermined time instantfollowing the start of the next sequential measuring pulse is comparedwith the corresponding value of a preceding measuring pulse and acomparison signal is generated as a function of the differencetherebetween. A terminating signal, terminating the application of thebrakes, is then furnished when the comparison signal corresponds to adifference exceeding a first predetermined difference. Such aterminating signal does not completely terminate a braking process thathas begun, but simply causes the brakes to be lifted for a short time.If the danger of a blocked wheel re-occurs, the process of terminatingthe braking operation repeats also.

As a further feature of the method of the present invention, it ispossible to cause the furnishing of the terminating signal to end ifcomparison of the above-mentioned instantaneous values indicates thatthe difference therebetween is less than a second predetermineddifference.

In this manner, the brakes are automatically disconnected only as longas a danger of locking exits. The process repeats automatically untilthe particular braking operation has ended.

The measuring pulses into which the pulses generated in synchronism withthe rotation of the wheels are reshaped, may either be of a sawtoothform or they may have a steep leading edge and a slowly decreasingtrailing edge. The last-named measuring pulse is particularly easy togenerate by means of a capacitor and resistors and particularlyfavorable operation results if the instantaneous values to be comparedoccur in the region of the trailing edge. The instantaneous values to becompared may be those values at which the steep leading edge of ameasuring pulse and the trailing edge of the previous measuring pulseare equal-or it may be those points in the trailing edge of themeasuring pulses which coincide with the beginning of the followingmeasuring pulse.

In a preferred embodiment of the present invention, the comparison ofthe two instantaneous values is accomplished by use of two monostablemultivibrators which are switched to the unstable state, by means of anauxiliary pulse. The amount of time in which the two monostablemultivibrators remain in the unstable state is determined by theamplitude of the instantaneous values to be compared. Thus the problemof determining the difference in time between two successive measuringpulses in order to determine the possibility of a locked wheel, is thussolved in a particularly simple manner.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construc tion and its methodof operation, together with additional objects and advantages thereof,will be best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows an arrangement of thepresent invention utilizing two storages and two monostablemultivibrators;

FIG. 2 shows an arrangement of the present invention using a singlestorage element; and

FIG. 3 shows the variation of several measuring pulses with respect totime.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Pulse generating means,fastened to the body of a vehicle in such a manner that a pulse sequenceis generated in synchronism with the rotation of a wheel, are denoted byreference numeral 10 in FIG. 1. The pulse generator 10 consists of amagnetic yoke 11, on which is fastened a winding 12. One terminal ofthis winding is connected to ground, while the other is connected withthe input of a pulse shaping network 13, which shapes the pulses intopulses having a standard height and length, independent of the pulserepetition rate. The network 13 consists for instance of an monostableswitch in connection to a Schmitt-trigger. The output of unit 13 issupplied to a unit 14 which comprises the means for reshaping the pulsesin the sequence into measuring pulses. Units 13 and 14 togetherconstitute pulse shaping means. Thus unit 14 furnishes a measuring pulsein response to each input pulse, this measuring pulse in response toeach input pulse, this measuring pulse having a steep leading edge and aslowly decreasing trailing edge. This unit may, for example, comprise acapacitor which is charged rapidly, that is with a low time constant,and to which is connected a long time constant discharge circuit, as,for example, a discharge resistance. The measuring pulses are then fedto switching means, labeled 15 in FIG. 1, which, as indicated by dashedline 16, are operated in synchronism with the pulses in the pulsesequence. The switching means may, for example, operate in synchronismwith the pulses at the output of unit 13. Switching means 15 have afirst and second output, leading respectively to a first and secondcomparator storage means, denoted by reference numerals 17 and 18,respectively. The output of the first comparator storage is connected tothe input of first monostable circuit means, for example a monostablemultivibrator 19, while the output of the second comparator storagemeans is connected to the input of the second monostable circuit means,denoted by reference numeral 20 in FIG. 1. Each of the two storage units17 and 18 furnishes a signal signifying the completion of a storageprocess. The signals are supplied to a delay unit 21 which in turnfurnishes an auxiliary signal switching the two monostablemultivibrators 19 and 20 into the unstable state. The auxiliary signalmay be furnished after a delay time adjusted in said delay means. Theamount of time that the two multivibrators remain in the unstable statedepend upon the amplitude of the signal stored in storages 17 and 18,respectively. The output of the two monostable multivibrators aresupplied to an output stage 22. Here it is determined by means of logiccircuits, whether the monostable multivibrator 19 returns to the stablestate prior or following the return to the stable state of monostablemultivibrator 20. The terminating signal is furnished by the outputstage 22, if a locking process is indicated.

In order to explain the arrangement in FIG. 1, it may be useful to referto the sequence of measuring pulses illustrated in FIG. 3. These are thepulses that appear at the output of unit 14. Up to time t1, the pulserepetition rate is constant or decreases relatively slowly. Thisindicates that the particular wheel turns with constant angular velocityor slows up somewhat during a normal braking process. Two sequentialmeasuring pulses are separated by a time interval tml. In the particularexamples shown, those instantaneous values of the measuring pulses arecompared which occur when the leading edge of a measuring pulseintersects the slowly decreasing trailing edge of the precedingmeasuring pulse, that is when the two values are equal. A time :2, wherea rather large delay has occurred, that is the distance tm2 between twoconsecutive measuring pulses, has increased considerably over thecorresponding distance tml occurring at time t1. Because of the kineticenergy stored in the turning wheel, the wheel cannot suddenly lockbetween two measuring pulses, but the two instantaneous values A1 and A2can differ so considerably, that a beginning of a locking process isindicated. Switching means shown in FIG. I serve to store theinstantaneous values to be compared (herein referred to as measuringsignals) alternately in storages l7 and 18. These values are denoted byAl and A2 in FIG. 3. Each time when a storing process has beencompleted, the relevant storage generates a signal from which theauxiliary signal is derived after a delay in the delay unit 21 whichprovides an adjustable delay. The auxiliary signal switches bothmonostable multivibrators, namely units 19 and into the unstable state.If no locking has occurred, the values stored in storages 17 and 18 aresubstantially equal, thus resulting in the fact that the monostablemultivibrators 19 and 20 remain in the unstable state for substantiallythe same time period. Therefore no terminating signal is furnished byoutput stage 22. If, however, a locking process is beginning, then thevalue Al may be stored in storage 17, while the value A2 is stored instorage 18. In this case the two monostable multivibrators will returnto the stable state at a different time interval. If this differenceexceeds a first predetermined difference, then the terminating signal isfurnished by the output stage 22. As soon as the difference between thetwo values is less than the second predetermined difference, theterminating signal is no longer furnished. In this way, a type ofhysteresis is generated which may be adjusted to correspond to theparticular vehicle and the particular tires in use. If, in thiscircuitry, the discharge resistor in unit 14 has a resistance whichvaries in dependence on the speed of the vehicle, then the trailing edgeof the measuring pulses will decrease even more slowly at low speedsthan at high speeds. As a result, great accuracy can be achieved overthe whole range of wheel rotational speed, since the values to becompared always occur within a region of sufficiently steep decrease ofthe trailing edge of the measuring pulse.

In an alternate embodiment of the present invention, it is possible tocompare instantaneous values not of two directly sequential measuringpulses, but of every third, fifth or every other, fourth or sixthmeasuring pulse may be compared. It is further possible that themonostable multivibrator are switched to the unstable state not afterthe storage in both storages has been completed, but after a new valuehas been entered into any one of the storages. Further, it is possibleto omit the delay unit; the monostable multivibrators are then switchedimmediately following the entering of a new value into one or bothstorages. If the time that the monostable multivibrators 19 or 20 are inthe unstable state is greater than the time between two measuringpulses, which is shown as !m in FIG. 3, which may occur at the highestspeed of the vehicle, then it is possible to break the connectionbetween the unit 14 and switching means 15 during one operating cycle ofthe output stage 22. After each operating cycle, the arrangementcomprising switching means 15, the two storages 17 and 18 and the twomonostable multivibrators 19 and 20, that is the comparator means, thenare reactivated for the subsequent operating cycle of the output stage22.

In FIG. 2, an embodiment of the invention is shown which requires only asingle storage. The output of unit 14, which serves to generate themeasuring pulses as does the same numbered unit in FIG. 1, is connectedto a gate 30. As indicated by the dashed line 31, this gate is operatedby the pulses generated by the pulse shaping means 13. The output ofgate 30 serves to supply the selected instantaneous values of themeasuring pulses to the storage 32, whose output is connected with acomparator element 33. The output of the comparator element 33 isconnected to a threshold element 34 at whose output the terminatingsignal is furnished if a particular threshold value has been exceededand is connected to one input of the comparator element 33, as shown bythe dashed line 35. This threshold value may be adjustable. Thisarrangement functions as follows: The instantaneous values of themeasuring pulses which are to be compared are furnished to storage 32via gate 30 and directly to the comparator element 33. If the wheelturns with a constant rotation speed, the stored values do not change.However, if the rotational speed decreases, so that the stored valueschange from the value indicated by A1 in FIG. 3 to that indicated by A2,then the comparator element 33 generates a signal resulting from thischange in amplitude, whose magnitude corresponds to a difference betweenthe two stored values. If this comparison signal exceeds the thresholdvalue to which unit 34 has been adjusted, then the terminating signal isfurnished. Similarly, this terminating signal is suppressed if thecomparison signal indicates that the difference in magnitude is lessthan a second predetermined threshold value.

The circuit unit for use as storages as shown in FIGS. 1 and 2 may beamplifiers which have an integrated circuit in the forward path. It isparticularly advantageous for the arrangement in FIG. 2, that theintegrating amplifier has a nonlinear characteristic, which causes theslope of the leading edge of the output signal to be independent of theamplitude of the input signal, that is the output signal will rise tothe value to be stored along the same sawtooth curve, independent of theinput signal. If such a storage is used, it is further advantageous thatthe subsequently connected comparator element comprises a monostablemultivibrator which is switched to the unstable state simultaneouslywith the beginning of each storage process. The time that the monostablemultivibrator remains in the unstable state then constitutes thethreshold value. If the monostable multivibrator returns to the stableposition before the storage process has been completed, then the speeddecrease in the wheel has exceeded the maximum allowable value, and aterminating signal is furnished.

Thus this invention allows the locking of the wheels to be prevented byuse of relatively little additional equipment and in a simple, reliable,and very rapidly operating form.

Thus the problem to measure the time interval between two consecutivemeasuring pulses and to derive a terminating signal from possiblechanges in this time period, is solved in a simple fashion by thecomparison of two instantaneous values in measuring pulses of a suitableform.

While the invention has been illustrated and described as embodied incircuits using monostable multivibrators, it is not intended to belimited to the details shown, since various modifications, circuitchanges and structural changes may be made without departing in any wayfrom the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. Arrangement for preventing locking of a wheel of a vehicle during abraking process, comprising, in combination, pulse generating means forgenerating a pulse sequence in synchronism with the rotation of saidwheel; pulse shaping means for shaping the pulses in said sequence intomeasuring pulses having substantially identical leading portions andindependently of speed substantially the same peak amplitudes and havingtrailing portions, the spacing of said pulses depending upon the speedof rotation of said wheel, each of said trailing portions having aportion overlapping in time with a portion of the leading portion of thenext sequential one of said measuring pulses; means furnishing measuringsignals corresponding to the instantaneous values of overlappingtrailing portions of said measuring pulses at predetermined time in- Istants within the corresponding overlapping leading portions of thefollowing measuring pulses; comparing means comparing at predeterminedtime intervals sequential measuring signals and generating comparisonsignals as a function of the differences between sequential measuringsignals; and terminating signal furnishing means for terminating theapplication of the brakes when at least one of said comparison signalscorresponds to a difierence exceeding a first predetermined difference.

2. An arrangement as set forth in claim 1, wherein said comparing meanscomprise first and second monostable circuit means, respectively adaptedto stay in the unstable state for a time period corresponding to a firstand second applied signal; auxiliary means for switching said monostablecircuit means simultaneously into said unstable state; and switchingmeans for alternately applying selected measuring signals to said firstand second monostable circuit means for constituting said first andsecond applied signals.

3. An arrangement as set forth in claim 2, further comprising first andsecond comparator storage means connected to the output of saidswitching means, said first and second storage means respectively havinga first and second storage output, said first and second storage outputconstituting said first and second applied signals.

4. An arrangement as set forth in claim 3, wherein said first and secondstorage means each comprise amplifier circuits having integratorcircuits in the forward path.

5. An arrangement as set forth in claim 1, wherein said pulse generatingmeans comprise a reactive reactance and means for changing the reactanceof said reactive circuit abruptly during the rotation of a wheel.

6. An arrangement as set forth in claim 5, wherein said reactance is aninductance.

7. An arrangement as set forth in claim 5, wherein said reactance is acapacitance.

8. An arrangement as set forth in claim 5, wherein said pulse shapingmeans comprise a capacitor, short time constant means for charging saidcapacitor, and long time constant discharge means for discharging saidcapacitor, whereby said measuring pulses comprise a steep leading edgeand a slowly decreasing trailing edge.

9. An arrangement as set forth in claim 8, wherein said long timeconstant discharge means comprise a resistance.

10. An arrangement as set forth in claim 9, wherein said resistance is avariable resistance, adapted to change in dependence on the speed ofsaid engine.

11. Method for preventing locking of a wheel of a vehicle during abraking process, comprising, in combination, the steps of generating apulse sequence in synchronism with the rotation of said wheel; reshapingthe pulses in said sequence into measuring pulses having substantiallyidentical leading portions and independently of speed substantially thesame peak amplitudes and having trailing portions, the spacing of saidpulses depending upon the speed of rotation of said wheel, each of saidtrailing portions having a portion overlapping in time with aportion ofthe leading portion of the next sequential one of said measuring pulses;furnishing measuring signals corresponding to the instantaneous valuesof overlapping trailing portions of said measuring pulses atpredetermined time instants within the corresponding overlapping leadingportions'of the following measuring pulses; comparing, at predeterminedtime intervals, sequential measuring signals and generating comparisonsignals as a function of the difference between sequential measuringsignals; and furnishing a terminating signal terminating the applicationof the brakes when at least one of said comparison signals correspondsto a difference exceeding a first predetermined difference.

12. A method as set forth in claim 11, further comprising the step ofending the furnishing of said terminating signal when said comparisonsignal corresponds to a difference less than a second predetermineddifference.

13. A method as set forth in claim 11, wherein said measuring pulsescomprise sawtooth pulses.

14. A method as set forth in claim 11, wherein said measuring pulseshave a steep leading edge and a relatively slowly decreasing trailingedge.

15. A method as set forth in claim 14, wherein said predetermined timeinstants are the time instant at which the instantaneous value of thesteep leading edge of a measuring pulse and the slowly decreasingtrailing edge of a previous measuring pulse are equal in value.

16. A method as set forth in claim 11, wherein said predetermined timeinstants are the beginnings of said following measuring pulses.

1. Arrangement for preventing locking of a wheel of a vehicle during abraking process, comprising, in combination, pulse generating means forgenerating a pulse sequence in synchronism with the rotation of saidwheel; pulse shaping means for shaping the pulses in said sequence intomeasuring pulses having substantially identical leading portions andindependently of speed substantially the same peak amplitudes and havingtrailing portions, the spacing of said pulses depending upon the speedof rotation of said wheel, each of said trailing portions having aportion overlapping in time with a portion of the leading portion of thenext sequential one of said measuring pulses; means furnishing measuringsignals corresponding to the instantaneous values of overlappingtrailing portions of said measuring pulses at predetermined timeinstants within the corresponding overlapping leading portions of thefollowing measuring pulses; comparing means coMparing at predeterminedtime intervals sequential measuring signals and generating comparisonsignals as a function of the differences between sequential measuringsignals; and terminating signal furnishing means for terminating theapplication of the brakes when at least one of said comparison signalscorresponds to a difference exceeding a first predetermined difference.2. An arrangement as set forth in claim 1, wherein said comparing meanscomprise first and second monostable circuit means, respectively adaptedto stay in the unstable state for a time period corresponding to a firstand second applied signal; auxiliary means for switching said monostablecircuit means simultaneously into said unstable state; and switchingmeans for alternately applying selected measuring signals to said firstand second monostable circuit means for constituting said first andsecond applied signals.
 3. An arrangement as set forth in claim 2,further comprising first and second comparator storage means connectedto the output of said switching means, said first and second storagemeans respectively having a first and second storage output, said firstand second storage output constituting said first and second appliedsignals.
 4. An arrangement as set forth in claim 3, wherein said firstand second storage means each comprise amplifier circuits havingintegrator circuits in the forward path.
 5. An arrangement as set forthin claim 1, wherein said pulse generating means comprise a reactivecircuit; and means for changing the reactance of said reactive circuitabruptly during the rotation of a wheel.
 6. An arrangement as set forthin claim 5, wherein said reactance is an inductance.
 7. An arrangementas set forth in claim 5, wherein said reactance is a capacitance.
 8. Anarrangement as set forth in claim 5, wherein said pulse shaping meanscomprise a capacitor, short time constant means for charging saidcapacitor, and long time constant discharge means for discharging saidcapacitor, whereby said measuring pulses comprise a steep leading edgeand a slowly decreasing trailing edge.
 9. An arrangement as set forth inclaim 8, wherein said long time constant discharge means comprise aresistance.
 10. An arrangement as set forth in claim 9, wherein saidresistance is a variable resistance, adapted to change in dependence onthe speed of said engine.
 11. Method for preventing locking of a wheelof a vehicle during a braking process, comprising, in combination, thesteps of generating a pulse sequence in synchronism with the rotation ofsaid wheel; reshaping the pulses in said sequence into measuring pulseshaving substantially identical leading portions and independently ofspeed substantially the same peak amplitudes and having trailingportions, the spacing of said pulses depending upon the speed ofrotation of said wheel, each of said trailing portions having a portionoverlapping in time with a portion of the leading portion of the nextsequential one of said measuring pulses; furnishing measuring signalscorresponding to the instantaneous values of overlapping trailingportions of said measuring pulses at predetermined time instants withinthe corresponding overlapping leading portions of the followingmeasuring pulses; comparing, at predetermined time intervals, sequentialmeasuring signals and generating comparison signals as a function of thedifference between sequential measuring signals; and furnishing aterminating signal terminating the application of the brakes when atleast one of said comparison signals corresponds to a differenceexceeding a first predetermined difference.
 12. A method as set forth inclaim 11, further comprising the step of ending the furnishing of saidterminating signal when said comparison signal corresponds to adifference less than a second predetermined difference.
 13. A method asset forth in claim 11, wherein said measuring pulses comprise sawtoothpulses.
 14. A metHod as set forth in claim 11, wherein said measuringpulses have a steep leading edge and a relatively slowly decreasingtrailing edge.
 15. A method as set forth in claim 14, wherein saidpredetermined time instants are the time instant at which theinstantaneous value of the steep leading edge of a measuring pulse andthe slowly decreasing trailing edge of a previous measuring pulse areequal in value.
 16. A method as set forth in claim 11, wherein saidpredetermined time instants are the beginnings of said followingmeasuring pulses.